1. Field of the Invention
The present invention relates to a scalable video decoder and a controlling method thereof, and more particularly, to a scalable video decoder that can reduce the usage amount of a memory when up-sampling a video block in scalable decoding of an image signal, and a controlling method thereof.
2. Description of Related Art
A scalable video codec (SVC) scheme denotes a scheme that encodes an image signal to the best quality. Also, although a partial sequence of resultantly generated picture sequence, that is, a sequence of a frame that is partially selected from all sequences, is decoded and used, the SVC scheme enables low quality video expression.
A hierarchical B picture (H-B picture) scheme is an encoding scheme that is proposed to be used for the above SVC.
The picture sequence, encoded using the H-B picture corresponding to the SVC scheme, receives and processes only the partial sequence to thereby enable the low quality video expression. However, when a bitrate is decreased, the quality may be even more degraded. In order to solve this problem, it is possible to hierarchically provide separate auxiliary picture sequences with a low transmission bitrate, for example, picture sequences with a low frame rate per second.
Also, up-sampling or down-sampling of an image may be required in order to simultaneously transmit a large image and a small image. Specifically, it is possible to encode a single image signal source into each of a four common intermediate format (CIF) picture sequence, a CIF picture sequence, and a quarter common intermediate format (QCIF) picture sequence, and transmit the encoded picture sequences to a decoding apparatus.
Since both an upper layer and a lower layer encode the same image signal source, redundancy exists in the encoded signal of both the upper layer and the lower layer.
Therefore, in order to increase a coding rate of a particular layer that is encoded according to a scheme of transmitting various types of screen sizes, an image frame of a current layer at the same point in time as an image frame of a lower layer is created as a predicted image, that is, residual data based on the image frame of the lower layer. For example, when encoding a current macro bloc of a high resolution image into an intra BL mode, a corresponding macro block of the lower layer, that is, a block including a region that corresponds to the same time as the current macro block and also corresponds to the same location in a frame is up-sampled and then a difference value between pixel values of the up-sampled block or an error value is encoded in the current macro block.
The up-sampled block is not transmitted to a decoder. Thus, so that the decoder may decode the encoded macro block, the decoder must up-sample a corresponding macro block of the lower layer and use the up-sampled macro block. The corresponding macro block of the lower block needs to be up-sampled not only for encoding the macro block of the intra BL mode, but also for performing a residual data prediction operation between layers.
As described above, when providing a plurality of layers with a different picture size or resolution from encoding streams, there is a need for up-sampling an image block during an encoding and decoding process.